In a known type of image forming apparatuses, which include printers, facsimile machines, copiers, and multifunction peripherals, image formation (which may involve recording, printing, transfer, etc.) is performed by discharging droplets of a recording fluid onto a medium (such as a sheet of paper or any other material, a recording medium, transfer material, a recording paper, etc.) using a liquid-discharging recording head while the medium is transported.
As used herein the term “image forming apparatus” is intended to refer to an apparatus that performs image formation by discharging droplets of a recording fluid onto a medium, which may be made of various materials, such as paper, threads, fibers, fabrics, leather, metals, plastics, glass, wood, and ceramics. As used herein the term “image formation” is intended to refer not just to the transfer of an image with some meaning, such as letters or a figure, to a medium, but also to the imparting of an image without any meaning, such as a random pattern, to the medium. As used herein the term “recording fluid” is intended to refer not just to ink but also any fluid that can be discharged in the form of droplets to perform image formation in the above sense.
In such a liquid-discharge type image forming apparatus, when image formation is performed by forming droplets of a recording fluid (to be hereafter referred to as an “ink”) including a colorant, problems known as feathering or color breeding may occur. The feathering is the blurring of an ink dot on the medium. The color breeding is the blurring of the boundary of different colors when ink droplets of different colors are sprayed onto the sheet adjacent to one another. Another problem associated with this type of an image forming apparatus is that a droplet placed on the sheet needs time to dry.
Japanese Laid-Open Patent Application No. 8-323977 discloses that a heating unit is used before or after printing to prevent blurring and promote the drying of sprayed ink.
Japanese Laid-Open Patent Application No. 2002-137378 discloses that a preprocessing fluid that reacts with ink to prevent blurring is applied to the sheet with a coating roller. Japanese Laid-Open Patent Application No. 2005-138502 discloses that a preprocessing fluid is sprayed out of a liquid discharge head in the form of mist to coat the sheet.
However, the use of a heating unit leads to an increase in power consumption. The coating of the sheet with a preprocessing fluid using a coating roller or a liquid discharge head may produce coating irregularities. The coating technology also has the problem of the extended time required for the fluid to dry after reacting with the ink on the sheet. The sheet may also curl or warp after the coating, resulting in the increased likelihood of jamming.